Ammines of chromium(II) acetate

Isolation of a hexanuclear chromium cluster with a tetrahedral hydridic core and its catalytic behavior for ethylene oligomerization

A chromium complex [2-(NHCH2PPh2)C5H4N]CrCl3·THF2 (1) of the ligand PyNHCH2PPh2 has been synthesized, characterized, and examined for its catalytic behavior toward ethylene oligomerization. When complex 1 was treated with (i-Bu)3Al, an unprecedented divalent polyhydride chromium cluster μ,κ(1),κ(2),κ(3)-N,N,P-{[2-(NCH2PPh2)C5H4N]Cr(μ-H)}4[(μ-Cl)Cr(μ-Cl)Al(i-Bu)2Cl]2 (2) was obtained. The complex contains a Cr4H4 core, which is expected to be diamagnetic, and which remains coordinated to two additional divalent high-spin Cr atoms via bridging interactions. Two aluminate residues remain bonded to the peripheral chromium atoms. The structure, magnetism, and electronic configuration are herein discussed.

A weak, short metal-metal bond in a chromium(II) amidinate complex

Treatment of chromium(II) chloride with 2 equiv of Li[tBuNC(CH3)NtBu], Li[iPrNC(CH3)NiPr], or Li[tBuNC(CH3)NEt] (prepared from the corresponding carbodiimides and methyllithium) afforded Cr[tBuNC(CH3)NtBu]2 (1, 50%), Cr[iPrNC(CH3)NiPr]2 (2, 54%), and [Cr(tBuNC(CH3)NEt)2]2 (3, 58%) as deep blue, purple, and amber or metallic green crystals, respectively. Cr[tBuNC(CH3)NtBu]2 and Cr[iPrNC(CH3)NiPr]2 possess monomeric structures in the solid state with tetrahedral and square planar geometries about the chromium centers, respectively. [Cr(tBuNC(CH3)NEt)2]2 exists as a dimer in the solid state, with two mu2-amidinate ligands, two eta2-amidinate ligands, and a chromium-chromium bond length of 1.9601(12) A. [Cr(tBuNC(CH3)NEt)2]2 is diamagnetic in the solid state, as determined by magnetic susceptibility measurement and CP/MAS 13C NMR spectroscopy. However, [Cr(tBuNC(CH3)NEt)2]2 dissociates into paramagnetic monomers in solution, as determined by observation of extremely broad peaks in the 1H NMR spectra in cyclohexane-d12 and benzene-d6, a solution magnetic moment measurement, and by solution molecular weight measurements in benzene. The combined results suggest that the chromium-chromium bond strength in [Cr(tBuNC(CH3)NEt)2]2 is weak and cannot exceed the difference in solvation energies between the dimer and two monomers, plus any increase in metal-nitrogen bond strengths in the monomers.

Preparation and Characterization of a Diamagnetic and Dinuclear Titanium(III) Formamidinate Complex. Evidence for the Existence of a Ti-Ti Bond?

The new diamagnetic Ti(III) complex (CyNC(H)NCy)(4)Ti(2)Cl(2).2THF (1) containing a short Ti-Ti distance was prepared and crystallographically characterized. Ab initio unrestricted Hartree-Fock calculations suggested the presence of a Ti-Ti bonding interaction. Crystal data for 1 are as follows: C(60)H(108)N(8)Ti(2)Cl(2)O(2), FW 1140.27, monoclinic Pn, a = 10.4688(9) Å, b = 14.4579(9) Å, c = 21.421(1) Å, beta = 100.227(9) degrees, V = 3190.6(7) Å(3), Z = 2, D(calc) = 1.187 g/cm(3), F(000) = 1236, &mgr; = 3.75 cm(-)(1), T = -158 degrees C, R = 0.074, R(w) = 0.075, GOF = 3.64 for 540 parameters and 4630 reflections out of 5771 unique reflections observed.